Films for ostomy applications should have good odor barrier properties and produce minimal noise when flexed or wrinked to avoid embarrassment to users. Typically, films currently in use for ostomy applications utilize polyvinylidene chloride (PVDC) or copolymers of vinylidene chloride with a comonomer such as methylacrylate or vinylchloride as the gas barrier layer of a multilayer film. Such multilayer films have good resistance to odor transmission and are also relatively quiet; however, they are also believed to be hazardous to the environment when disposed of by incineration, a common practice in numerous countries. Chlorinated polymers generate hydrochloric acid as a byproduct of incineration and are believed to be a significant contributor to hydrochloric acid release from incinerator flue gases. Furthermore, chlorinated polymers are believed to form toxic dioxin derivatives as byproducts of incineration which are retained in the ashes and may possibly cause solid waste disposal problems.
Unfortunately, films formed of chlorine-free barrier resins tend to be stiffer and noisier than films utilizing conventional PVDC-based resins and do not match the quality of conventional chlorinated films for use in ostomy appliances. Thus, a need exists for a multilayer film which is chlorine-free, can be manufactured by coextrusion from readily available raw materials, is heat sealable, has high softness and low noise when flexed or wrinkled, and is impermeable to fecal odors.
U.S. Pat. No. 5,567,489 discloses a multilayer barrier film in which a chlorine-free barrier layer is composed of amorphous nylon, crystalline nylon, copolymers of ethylene and vinyl alcohol, or blends thereof. Although data presented in the patent indicate the multilayer films to be comparable in quietness to some chlorinated films in general commercial use, experience has revealed that such chlorine-free films are nevertheless significantly noisier than the chlorine-containing films commonly employed for the fabrication of ostomy pouches. The general observation is that unmodified nylon resins are high modulus, stiff materials that do not lend themselves to the production of low noise ostomy films. This is true of all nylon (polyamide) barrier resins, both crystalline and amorphous.
A further disadvantage of unmodified nylon resins is that they are generally incompatible with typical resins used for the heat-sealable outer skin layers and necessitate the use of intermediate adhesion-promoting tie layers between a nylon barrier layer and such skin layers. For example, U.S. Pat. No. 5,567,489 discloses the use of tie layers formed of copolymers of ethylene and vinyl acetate, or copolymers of ethylene and acrylic acid, to improve the adhesion between the core and skin layers. The result is a multilayer film having at least five layers, at least in those embodiments in which two outer skin layers are provided.
Other references illustrating the current state of the art relating to chlorine-free multilayer films are U.S. Pat. Nos. 5,496,295, 5,643,375, and 5,407,713.
One aspect of this invention lies in the discovery that if an odor-barrier layer of a chlorine-free multilayer film is composed of a blend of nylon (polyamide) resin with an ionomer resin, instead of straight nylon, stiffness is significantly reduced and film structures can be produced with lower noise than those containing unmodified nylon. Surprisingly, it has been found that the reduction in noise can be achieved with no measurable loss in odor barrier properties. A further advantage of using a nylon-ionomer resin blend is that unlike unmodified nylons which necessitate the use of intermediate adhesion-promoting tie layers between a nylon barrier layer and the outer skin layers, ionomer-modified nylons have good compatibility and provide excellent adhesion to polyacrylate-type skin layer resins, thus allowing the fabrication of multilayer films (with two outer skin layers) of a total of three rather than five layers. It has been found that high interfacial adhesion can be achieved even at low levels of ionomer in the blend.
The nylon barrier layer may be composed of either an aliphatic or a partially aromatic polyamide, or a blend thereof, blended with an ionomer resin consisting essentially of a partially neutralized ethylene-methacrylic acid copolymer. Nylon/ionomer blends ranging from 30 to 90% nylon and 70 to 10% ionomer by weight are believed effective, with the preferred ratios falling in the range of 50 to 70% nylon and 50 to 30% ionomer.
The multilayer chlorine-free film includes at least one heat-sealable skin layer, preferably two such skin layers, coextruded with and directly contacting the blended nylon/ionomer barrier layer. Each skin layer is composed of a copolymer of ethylene and an ester-containing comonomer such as methyl acrylate, ethyl acrylate, butyl acrylate or vinyl acetate. Preferably, the skin layer composition is a resin composed of a copolymer of ethylene and methyl acrylate (EMA) having a methyl acrylate content in the range of about 10 to 30% by weight.
The result is a multilayer heat-sealable chlorine-free film particularly suitable for the fabrication of ostomy pouches and other waste collection pouches because of its effective odor barrier properties, relatively low noise when flexed or wrinkled, low modulus or high softness, and high interlaminar strength even when no tie layers are used. The ionomer content of the modified nylon barrier layer promotes strong resistance to delamination, and the heat sealability of the skin layer or layers assures that the walls of a pouch formed of such multilayer film may be securely welded to each other by heat sealing, including RF sealing. A pouch formed of the multilayer film of this invention therefore has properties comparable to those exhibited by high-quality pouches formed of chlorine-containing compositions but without the environmental shortcomings described above.
Other features, advantages and objects of the invention will become apparent from the specification and drawings.